1. Field of the Invention
The invention relates to a magnetoresistive effect element for reading out a magnetic field intensity as a signal in magnetic substances such as magnetic medium.
2. Description of the Related Art
Recently, there has been developed the improvement of sensitivity of a magnetic sensor and the densification in magnetic recording, and following such development, there has also developed a magnetoresistive effect type magnetic sensor (hereinafter, referred to simply as a MR sensor) and a magnetoresistive effect type magnetic head (hereinafter, referred to simply as a MR head). Both of a MR sensor and a MR head read out external magnetic field signals in accordance with a change in a resistance of a reading sensor composed of magnetic material. Both of a MR sensor and a MR head have a characteristic that a relative speed to a recording medium is not dependent on generated outputs. Hence, a MR sensor can obtain a high sensitivity, and a MR head can obtain a high output even in highly densified magnetic record.
Japanese Patent Public Disclosure No. 4-218982 laid open to the public on Aug. 10, 1992 has suggested an artificial lattice magnetoresistive effect layered structure which has a multilayered structure composed of a magnetic layer and a non-magnetic layer successively deposited and which exhibits a large change in magnetic resistance generated even for a small external field. In this artificial lattice magnetoresistive effect layered structure, a magnetic layer has a different coercive force from that of a magnetic layer deposited adjacent thereto via a nonmagnetic layer. A magnetoresistive effect element disclosed in the above mentioned Disclosure exhibits a few percents to tens of percents of resistance change rate even for an external magnetic field having an intensity ranging from a few of Oe to tens of Oe.
Though the magnetoresistive effect element can operate even with a small external magnetic field, it is necessary to apply an external bias magnetic field to the magnetoresistive effect element to obtain symmetrical regenerated waveforms of signals, if the magnetoresistive effect element is to be used as a practical sensor or magnetic head.
There has been reported another magnetoresistive effect layered structure in Physical Review B, Vol. 43, No. 1, 1991, page 1297, published by The American Physical Society. This magnetoresistive effect element has a structure comprising at least two thin magnetic layers separated by a non-magnetic thin interlayer. Adjacent to one of the soft thin magnetic layers is disposed a thin antiferromagnetic layer to provide anti-magnetic force thereto to thereby cause rotation of magnetization therein with an external magnetic field which is different from that of the other soft thin magnetic layer disposed adjacent to the one of the soft thin magnetic layer via a non-magnetic layer. Thus, a change in resistance is caused.
The above mentioned report has suggested, as a practical MR head, a magnetoresistive effect element having a structure comprising a soft magnetic layer, a non-magnetic insulator, a multlayered structure, a non-magnetic insulator and a soft magnetic layer successively deposited in this order. However, the magnetoresistive effect element has problems such that regenerated waves have a quite asymmetrical waveform, and that there is a fear that the magnetoresistive effect element may corrode because the magnetoresistive effect element is exposed to an ABS plane. If a magnetoresistive effect element is designed so that it is separated from the ABS plane, and an external magnetic field is introduced to the magnetoresistive effect element through a soft magnetic yoke, the symmetry of regenerated waveforms are considerably improved to thereby eliminate a fear of the corrosion of the magnetoresistive effect element.